Just wish I had an old iPhone laying around.
In the past I have purchased GoPhones and then removed the SIM card before turning them on. Then requested that the GoPhone be unlocked through this link:
https://forums.androidcentral.com/e...Fwww.att.com%2Fdeviceunlock%2F&token=QJE46aUz
Select that you are not an AT&T customer even if you are. I have always gotten an unlock code emailed to me within a few days. Then follow the instructions to unlock the phone but don't put a SIM card in the phone until it is unlocked. After it is unlocked, then you can put your postpaid SIM in the phone.
That may be a way to get a cheap backup phone.
You may not even have to get it unlocked to use it on AT&T postpaid, maybe you can just put your AT&T postpaid SIM in a GoPhone, I am not sure because I am on Verizon. But I always get GoPhones unlocked before activation.
If you are on TMobile and get the GoPhones unlocked, you can use them on TMobile.